Part 4

From the power box switch, go through the door. Turn on the lights in the dark hallway by using the switch to the left of the door.

Push the barrel at the end of the hallway out of your way. Turn right, climb the ladder, and go along the metal walkway to a door.

Past the door, wait for the G-Man to ride by on a tram. Once the light above the button to the right of the walkway bridge turns green, use the button to lower the bridge.

Cross the bridge, go through the door on the right, and up the stairs to the ba_elevator section.

Go through another door to reach the Sector G tram station. Enter the waiting room and follow the wall stripe to the elevator.

Use the large panel to the left of the elevator doors to help the scientists.

Stand away from the black scientist and wait for the elevator to descend. After it crashes and aliens teleport in, the "Duty Calls" chapter will start.

Exit the elevator, pick up the crowbar, and switch to the pistol. Go right and kill the two houndeyes near the stairs.

Bash boxes near the elevator; one contains a bullet clip, and a first aid station is behind another.

Bash boxes along the hallway around the stairs and look on a shelf for another bullet clip.

Continue bashing boxes until you reach a room with a power box on the back wall. Bash boxes to the right of the doorway to find another bullet clip, then shoot the power box.

Use your flashlight to find your way back to the stairs, go down them, and through the formerly locked door.

Crouch-walk into the room with the toxic waste spill, looking right to sneak-shoot two headcrabs.

Jump onto the big table, run across it, and jump to the floor on the other side. Turn right and shoot the headcrab behind the other table.

Push open the door and notice the headcrab next to a green barrel. Move into the room just enough for it to see you, then back up and shoot it.

Check the shelf in the back of the room for two bullet clips. Climb the ladder to the right of the shelf to reach a red-lit area with a scientist.

Crouch-walk to the scientist. Look left and shoot the explosive barrels on the other side of the locked fence door below.

Alternatively, to get past the fence door: move close to it without falling, jump to the light fixture on the wall above, crouch-drop onto the door, and drop down.

For another alternative: climb back down to the storage room, leave it, and go to the fence door. Pull the movable office chair out of the toxic liquid.

Get the chair next to the door, then jump-crouch onto it. From there, jump-crouch over the door and drop down on the other side.

Use your flashlight along the walkway past the fence door. Reach a small conveyor lift with a button panel. Use the panel and get on the lift.

Shoot the houndeyes that run into view on the walkway as you move toward them.

Get off the lift and go straight for the small door to the right of the big "NORTH TUNNEL" door.

Look right for a control console. Use the working button panel on the right end.

Stand in the doorway and watch the big south tunnel door until it stops opening. Quicksave.

As you run for the south tunnel door, a vortigaunt will teleport in. Swerve to hit it once with the crowbar to interrupt its charge-up, then run for the left side of the door.

Make it through the door and around the crates to section ba_canal2 without getting zapped. If not, quickrestore and try again.